ABSTRACT Encephalitis is a devastating disease causing significant morbidity and mortality. Critically, the etiology of > 60% of cases in the United States cannot be determined, posing significant challenges for patient management. Recently, viruses in the family Astroviridae have emerged as potential causes of encephalitis. Traditionally, astrovirus infection in humans has typically been associated with gastrointestinal disease. In the past several years, a number of novel astroviruses highly divergent from the classic human astroviruses have been discovered in human stool. Astrovirus VA1 (VA1) was discovered in 2009 in an unexplained outbreak of gastroenteritis. Subsequent serological studies have demonstrated that human infection with VA1 is common, with ~ 65% of the adult population harboring antibodies. Recently, four independent case reports have detected VA1 RNA in brain tissue of immunocompromised patients with encephalitis, suggesting that VA1 plays a causal role in encephalitis. In addition, another recent study identified human astrovirus serotype 4 in brain tissue of a transplant recipient with encephalitis. Together, these cases clearly demonstrate a previously unrecognized neurotropism of astroviruses and strongly implicate astroviruses as emerging causes of encephalitis in the immunocompromised. While the classic human astroviruses can be grown in a number of common cell lines, such as CaCo-2, Vero, and BHK, there have been no reports to date of a cell culture system for VA1. Furthermore there is currently no mouse model suitable for propagation of VA1, or for any human astroviruses. Currently, the fundamental barrier to understanding the mechanisms of neuropathogenesis of VA1 is the lack of a cell culture system and animal model. To address this limitation, complementary approaches will be taken to establish cell culture and murine animal model for propagation of VA1. Aim 1 will establish a cell culture system for VA1 while Aim 2 focuses on development of a mouse model for propagation of VA1 utilizing highly immunodeficient mice.